1. Technical Field
The present invention relates to a liquid crystal device and an electronic apparatus having the liquid crystal device.
2. Related Art
Fringe-field switching (FFS) mode liquid crystal displays (LCDs) have been developed to compensate for low aperture ratio and low transmissivity of in-plane switching (IPS) mode LCDs.
FIG. 11 is a plan view of a known FFS mode LCD. As shown in FIG. 11, a plurality of gate lines 200 and data lines 202 are arranged on a first transparent insulating substrate (not shown) in such a manner that they intersect each other and define unit pixels. Thin film transistors 204 are provided at the intersections of the gate lines 200 and the data lines 202. Plate-shaped common electrodes (not shown) are provided in the pixel regions defined by the gate lines 200 and data lines 202 arranged to intersect each other.
Pixel electrodes 206 are provided in the pixel regions. The pixel electrodes 206 are electrically insulated from the common electrodes and in contact with the thin film transistors 204. Each pixel electrode 206 has a plurality of slits, namely, a reference slit S1 that extends parallel to the gate lines 200 and is provided in the middle of the pixel in the longitudinal direction, a plurality of upper slits S2 arranged at a predetermined angle with respect to the reference slit S1, and a plurality of lower slits S3 arranged at a predetermined angle with respect to the reference slit S1.
Common signal lines 208 for applying common signals to the common electrodes are provided at edges of the pixels, adjacent to and parallel to the gate lines 200. The common signal lines 208 are partially in contact with the common electrodes, and partially overlap the pixel electrodes 206.
A color filter substrate (not shown) is arranged at a predetermined distance from the above-described array substrate. The color filter substrate includes a second transparent insulating substrate and predetermined elements, including a black matrix and color filters, formed thereon. A liquid crystal layer (not shown) containing positive or negative liquid crystal molecules is disposed between the first and second transparent insulating substrates.
A first horizontal alignment film and a second horizontal alignment film are provided on the inner surfaces of the array substrate and the color filter substrate, respectively. A first polarizing plate and a second polarizing plate are provided on the outer surfaces of the array substrate and the color filter substrate, respectively.
The first and second horizontal alignment films are rubbed in the direction parallel to the gate lines 200 when a positive liquid crystal is used, and in the direction parallel to the data lines 202 when a negative liquid crystal is used. The first and second polarizing plates are disposed in such a manner that their transmission axes are perpendicular to each other, to allow the LCD to operate in a normally black mode. One of the first and second polarizing plates is disposed in such a manner that its transmission axis is parallel to the rubbing axis of the alignment film.
In the above-described FFS mode LCD, the distance between the array substrate and the color filter substrate is larger than the distance between the common electrodes and the pixel electrodes 206. Thus, when an electric field is generated between the common electrodes and the pixel electrodes 206, a fringe field is generated between and above the two electrodes. Because the fringe field is generated over the entire region including a region above the common electrodes and the pixel electrodes 206, when the device is driven, not only the liquid crystal molecules between the common electrodes and the pixel electrodes 206, but also the liquid crystal molecules positioned above the two electrodes are operated.
In the FFS mode LCD, both the common electrode and the pixel electrode are made of a transparent conductive film. Thus, the FFS mode LCD has a high aperture ratio. Further, because the liquid crystal molecules above the electrodes are operated, the FFS mode LCD has high transmissivity. Further, symmetrical electric fields are formed in one pixel region or adjoining pixel regions, the refractive index anisotropy of liquid crystal molecules is corrected. Thus, color misalignment is prevented from occurring (for example, refer to JP-A-2002-182230).
As described above, the FFS mode LCD has the advantages that it has a high aperture ratio and high transmissivity. Further, it prevents color misalignment from occurring. However, the FFS mode LCD has the following disadvantages. When the rubbing axis is inclined 30 degrees or 45 degrees, the edge portions of the slits S2 and S3 in the pixel electrodes 206 become acute. This makes the electric fields in the slits be oriented in a plurality of directions, when a fringe field is generated between the common electrodes and the pixel electrodes 206. This causes some liquid crystal molecules to be oriented in directions slightly different from the direction in which the other liquid crystal molecules are oriented. Display defects, called disclinations, are produced at the boundary regions between these liquid crystal molecules oriented in directions slightly different from the direction in which the other liquid crystal molecules are oriented. When the display defects are produced in the display region, the transmissivity is decreased.
The FFS mode LCD has the slits S1, S2, and S3 in each pixel electrode 206. In this structure, the width W of the slits is narrow, or the distance L between the slits is large. At a portion where the width of the electrode is large, for example, the transmissivity tends to decrease, as in the case of IPS mode LCDs. Accordingly, it is difficult to produce LCD panels having good characteristics. In addition, there are some points where the movements of the liquid crystal molecules are different. In these regions, the transmissivity decreases.